1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of Related Art
Conventionally, in an electrographic image forming apparatus, an image is formed by forming a toner image on an image carrier such as a photoconductor drum, an intermediate transfer belt or the like based on image data, transferring the toner image on a paper, and fixing the toner image which is transferred on the paper by heating/pressuring. When there is a large amount of toner, paper wraps around the image carrier at the time of transferring and it becomes difficult to separate the paper from the image carrier. Specifically, in a case of a full-color image forming apparatus, toners of plurality of colors (yellow, magenta, cyan and black) are layered. Therefore, adhesion amount of toner to a paper becomes large and the wrapping of paper can occur easily.
In order to prevent this wrapping of paper, normally, the maximum value of YMCK data is set at the time when the color conversion process of converting RBG data to YMCK data is carried out so that the YMCK data after conversion does not exceed the maximum value. In a case where the image is all black, the output is controlled so as to be held down to 250% as a whole, for example, while the output should be total of 400% in which all of YMCK have output of 1000, normally.
Moreover, when toner is not enough to fill unevenness of paper surface, image quality is degraded. Therefore, there is suggested an image forming apparatus in which adhesion amount of toner is increased as the roughness of paper surface becomes greater (JP 2004-258397).
Further, there is suggested an image forming apparatus in which environmental condition such as temperature, humidity and the like of the place where the image forming apparatus is set is detected and in which the maximum value of amount of toner per unit area to be used at the time of printing to a print medium is changed according to the detection signal (JP 2004-78025).
Meanwhile, the easiness of occurrence of wrapping of paper to the photoconductor drum or the intermediate transfer belt differs according to type of the paper. For example, the wrapping tends to occur easily when the paper is a thin paper, and further, the wrapping tends to occur easily when the paper is in large size. Conventionally, a color conversion process condition is uniformly set by setting a paper which can be wrapped around easily as a basis. Therefore, color conversion process in which density is held down more than needed has been carried out to a paper of paper type which does not cause the wrapping. Thus, there is a problem that color gamut which can be reproduced becomes narrow in a case where a paper of a paper type in which the adhesion amount of toner does not need to be hold down is to be used.
Furthermore, conventionally, color conversion process condition is set uniformly by setting an image in which the wrapping can occur easily as a basis, that is, by setting an image in which adhesive amount of toner is greater as a basis. Therefore, color conversion process in which density is held down more than needed has been carried out to the image having density which does not cause the wrapping. Thus, there is a problem that color gamut which can be reproduced becomes narrow when forming an image in which the adhesive amount of toner does not need to be held down.